As someone with a constant vitamin D insufficiency I'd like to remind people that absorbtion is very difficult - you have to take it with a fatty meal!
> The presence of fat in a meal with which a vitamin D-3 supplement is taken significantly enhances absorption of the supplement [1]
> The presence of fat in a meal with which a vitamin D-3 supplement is taken significantly enhances absorption of the supplement [1]
1 - https://www.ncbi.nlm.nih.gov/pubmed/25441954